510 PSYCHOLOGY. 



case of simple paresis with apparent translocation oi the 

 field. 



Here the right eye succeeds in fixating the object, but 

 observation of the left eje will reveal to an observer the 

 fact that it squints just as violently inwards as in the former 

 case. The direction which the finger of the patient takes 

 in pointing to the object, is the direction of this squinting 

 and covered left eye. As Graefe says (although he fails to 

 seize the true import of his own observation), " It appears 

 to have been by no means sufficiently noticed how signifi- 

 cantly the direction of the line of sight of the secondarily 

 deviating eye [i.e., of the left,] and the line of direction of 

 the pointed finger agree." 



The translocation would, in a word, be perfectly ex- 

 plained could we suppose that the sensation of a certain 

 degree of rotation in the left eyeball were able to suggest 

 to the patient the position of an object whose image falls 

 on the right retina alone.* Can, then, a feeling in one eyo 



* An illusion in principle exactly analogous to that of the patient under 

 discussion can be produced experimentally in anyone in a way which 

 Heriug has described in his Lehre von Biuocularen Sehen, pp. 12-14. 1 wiU 

 quote Helmhoitz's account of it, which is especially valuable as coming 

 from a believer in the InnervationsgefuM: "Let the two eyes first look 

 parallel, then let the right eye be closed whilst the left still looks at the in- 

 finitely distant object a. The directions of both eyes will thus remain un- 

 altered, and a will be seen in its right place. Now accommodate the left 

 eye for a point / [a needle in Hering's experiment] lying on the optical 

 axis between it and a, only very near. The position of the left eye and its 

 optical axis, as well as the place of the retinal image upon it . . . are 

 wholly unaltered by this movement. But the consequence is that an ap- 

 parent movement of the object occurs— a movement towards the left. A3 

 soon as we accommodate again for distance the object returns to its old 

 place. Now what alters itself in this experiment is only the position of the 

 closed right eye : its optical axis, when the effort is made to accommodate 

 for the point/, also converges towards this point. . . . Conversely it is 

 possible for me to make my optical axes diverge, even with closed eyes, so 

 that in the above experiment the right eye should turn far to the right of 

 M. This divergence is but slowly reached, and gives me therefore no 

 illusory movement. But when I suddenly relax my effort to make it, and 

 the right optical axis springs back to the parallel position, I immediately 

 see the object which the left eye fixates shift its position towards the left. 

 Thus not only the position of the seeing eye a, but also that of the closed 

 eye b, influences our judgment of the direction in which the seen object 



